Stencil sheet and method of making an imaged stencil sheet

ABSTRACT

A STENCIL OF THE TYPE INCLUDING AN INK-IMPERVIOUS COATING OF A HEAT-FLOWABLE COMPOSITION OF THERMOPLASTIC FILM-FORMING MATERIAL COMPRISING A CELLULOSE ORGANIC ESTER, AND PLASTICIZING MATERIAL PARTIALLY BUT INCOMPLETELY COMPATIBLE WITH THE FILM-FORMING MATERIAL, INCORPORATES A POLYMERIC HYDROCARBON RESIN IN THE COATING THEREOF FOR MINIMIZING OIL TRANSFER FROM THE STENCIL. THE STENCIL SHEET MAY BE IMAGED THERMOGRAPHICALLY AND ALSO MECHANICALLY IN PREFERRED EMBODIMENTS.

United States Patent Oflice 3,8z41 l6 Patented July 16, 1974 17 Claims ABSTRACT OF THE DISCLOSURE A stencil sheet of the type including an ink-impervious coating of a heat-fiowable composition of thermoplastic film-forming material comprising a cellulose organic ester, and plasticizing material partially but incompletely com patible with the film-forming material, incorporates a polymeric hydrocarbon resin in the coating thereof for minimizing oil transfer from the stencil. The stencil sheet may be imaged thermographically and also mechanically in preferred embodiments.

RELATED APPLICATION This is a continuation-in-part of application Ser. No. 27,135, filed Apr. 9, 1970, now US. Pat. No. 3,704,155.

BACKGROUND OF THE INVENTION This invention relates to a stencil sheet of the type which includes a layer of a heat-flowable composition and to a method of making an imaged stencil sheet therewith by subjecting image areas of the stencil sheet to heat generated by infrared ray absorption.

US. Pat. No. 3,694,245, granted Sept. 26, 1972, on application Ser. No. 136,373, filed Apr. 22, 19.71, by the present inventors as a continuation-in-part of Ser. No. 674,153, filed Oct. 10, 1967 and now abandoned, discloses a thermographic stencil sheet including an ink-per-vious base sheet and an ink-impervious coating thereon of a heat-flowable composition of cellulose organic ester filmforming material and plasticizing material partially but incompletely compatible with the film-forming material. The stencil sheet is now in widespread commercial use. It is employed preferably in a stencil sheet assembly including a contacting absorbent sheet on one surface thereof, and a more rigid backing sheet on the opposite surface thereof and to which the absorbent sheet and the stencil sheet are mounted. In use, an original, such as a typed or printed sheet, is inserted between the stencil sheet and the backing sheet, and the assembly is exposed to infrared radiation on the face side of the absorbent sheet in a thermal copier such as a Weber Thermal Imager (Weber Marking Systems) or a Thermo-Fax machine (3M Company). Heat is generated in the radiation absorptive graphic portions of the original to cause the stencil sheet composition to flow in corresponding areas and thereby produce corresponding image openings in the stencil sheet. A portion of the composition rendered flowable is absorbed by the absorbent sheet and/or adjoining areas of the stencil sheet. The original and the absorbent sheet are separated from the imaged stencil sheet, the stencil sheet and the backing sheet are placed on a mimeograph duplicating machine followed by separation of the back- .ing sheet, and the machine is operated to produce multiple mimeograph copies of the original.

It was found in use that oil was transferred from the stencil sheet to the original in the image areas. The oil frequently broadened and feathered the copy on the typed original (smudging), and the presence of oil on the original was not a desirable condition. The smudging of the original affected the imaging speed in subsequent exposures, owing to the broadening of the image characters or transfer from the original to the stencil sheet. Subsequent performance was affected when the original was removed from the file for rerun, or in the event that optimum exposure was not used in imaging the first stencil.

It would be desirable to reduce the oil transfer to more desirable limits while preserving the advantageous properties of the stencil sheet of our aforesaid application.

In copending US. Pat. application Ser. No. 27,135, filed Apr. 9, 1970 by the present inventors, an improved thermographic stencil sheet exhibiting low oil transfer is claimed. The stencil sheet includes a heat-fiowable composition that forms a cooled melt having a limited pourable liquid volume, and plasticizing material in the composition having limited tack and aniline point.

The improved stencil sheet claimed in the latter copending application has markedly improved oil transfer prop erties and in many cases also provides improved copy quality. Nevertheless, there remains room for improve- SUMMARY OF THE INVENTION The present invention provides an improvement in a stencil sheet of the type disclosed in our application Ser. No. 136,373, which reduces oil transfer while maintaining and in many cases exceeding other prior performance characteristics.

In the invention, a thermoplastic polymeric hydrocarbon resin is incorporated in and forms a part of the heattlowable coating composition of a stencil sheet of the type disclosed in application Ser. No. 136,373. As in such prior application, the resulting composition includes a thermoplastic film-forming material comprising a cellulose organic ester, and plasticizing material partially but incompletely compatible with the film-forming material. The hydrocarbon resin functions in the composition both as a plasticizer for the cellulose ester and as a film-forming material, having, however, substantially lower film-forming strength than the cellulose ester. Therefore, the hydrocarbon resin is treated as a plasticizer while taking into account its film-forming properties in formulating a coating composition.

The stencil sheet of the present invention more particularly comprises an ink-pervious base sheet, and an inkimpervious coating thereon of a heat-fiowable composition of a cellulose organic ester film-forming material, and plasticizing material partially but incompletely compatible with the film-forming material including a thermoplastic polymeric hydrocarbon resin having a total content of polymerized indenes and coumarones of at least about 30% by weight.

The invention also provides a method of making an imaged stencil sheet, wherein the new stencil sheet is employed in contact with a graphic original, image areas of the stencil sheet are subjected to heat generated in the original by infrared ray absorption to render the composition flowable in the stencil sheet image areas, and the composition is caused to flow from the image areas and thereby form corresponding ink-transmitting image openings in the stencil sheet. Preferred embodiments of *theinvention also, or alternatively, may be imaged mech anically.

A stencil sheet may be provided according to the pres- 'enthinv'entio'n that reduces oil transfer to the lower level thus far achieved, the oil transfer being but a very small proportion of the transfer resulting from use of the pre- -ferred embodiments of application Ser. No. 136,373. Also,

the invention in its preferred embodiments for thermographic imaging affords a marked increase in stencil sheet durability. At the same time, copy quality is maintained, and imaging'speed is maintained and at times increased.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The stencil sheet of the invention includes a stencil base tissue sheet that may be formed of any suitable fiber, such as abaca fiber, abaca and wood fibers, kozo fiber, or polyester fiber, loosely arranged to provide a foraminous, highly permeable tissue. The tissue may weigh about 4 /2 to 12 pounds per 3,000 sq. ft. (24" by 36," 500 sheets). A heat-flowable coating composition, which is solid at ambient temperature, is applied to the base sheet at a rate of about 14 to 24 lbs. (dry basis),

sition on a stencil sheet visibly melts or liquefies.)

The heat-flowable coating composition includes a cellu- "lose organic ester film-forming material, which is capable of forming a continuous, cohesive, flexible, ink-impervious film. The cellulose ester melts or is plasticizable to melt in the range of about 65-180 C. Lower alkanoic acid esters of cellulose, especially 2- to S-carbon acid esters are preferred. The preferred cellulose esters include cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate valerate, cellulose propionate butyrate, cellulose propionate valerate, cellulose butyrate valerate, cellulose propionate, cellulose butyrate, and cellulose valerate. The cellulose ester preferably is employed in a proportion in the range of about 5-45 by volume (6- 52% by weight), and more preferably about 1430% by volume (16-36% by weight) of the coating composition, including the film-foming and plasticizing materials and exclusive of additives thereto. (It has been found in practice, consistent with theoretical considerations, that volume proportions are more significant than weight proportions when substitutions of one component for another are being considered. Accordingly, the propor tions of the ingredients of the coating composition for the most part are set forth herein by volume.) The preferred cellulose esters have a minimum total butyryl and valeryl content of about 35% by weight and a maximum ,hydroxyl content of about 4.7% by weight. The most advantageous results are obtained by employing higher total butyryl and valeryl contents, at least about 44% byweight, .and lower hydroxyl contents, about 2% by weight maximum. Optimally, the total butyryl and valeryl content is at least about 48% by weight, and the hydroxyl content is below about 0.7% by weight.

Cellulose acetate butyrate is the currently preferred cellulose ester, because it both furnishes a high quality product and is readily available in the market. Of the available grades of cellulose acetate butyrate, it is pre- 4 grades have viscosities of about 0.07 6 "seconds by A.S.T.M. Method D1343-54T in Formula A, A.S.T.M. Method D87154T, and melting or softening points ranging from C.,to 185. C., preferably, at least about C. .(determined as the temperature atwhich asamplefirstappearswet.) i

The cellulose ester film-forming-material iscembiflfid in the' coating composition with a plasticizing;v material partially but incompletely compatible. therewith; .Such

,plasticizing' material is defined to mean material which when heated with the film-forming material in the proportions used forms a substantially homogenous single 'phase melt, and which when cooled from the melt to ambient or room temperature forms a two-phase mixture, at least one phase of the mixture incorporating substantial proportions of both the film-forming material and the plasticizing material.

The preferred embodiments of the coating composition of film-forming and plasticizing materials exhibita transition between a single-phase mixture and a two-phase mixture at a temperature generally in the rangeof about 50-180 C. Such transition temperature is. referred to herein as the compatibility temperature of the composition, and it is determined as the cloud, point upon cooling the composition from a'single phase melt. Thus the first appearance of cloudiness signifies the transition from a single phase to two phases. In general, the transition is from a clear liquid to'a cloudy liquid, but an obscuring material may be present Without affecting performance.

Upon cooling below the compatibility temperature,

the separation into two phases continues. The mixture remains fluid over a temperature range, and then the phase containing the major proportion of the film-forming material gradually hardens to a solid as the. coating cools to room temperature. The remaining phase may solidify or remain liquid at room temperature. In the preferred embodiments, the remaining phase is a liquid at room temperature, forming a solid-liquid two-phase mixture thereat. The liquid phase may be trapped by the gel structure of the solid phase, or it may separate into a discrete liquid component. H

As disclosed in application Ser. No. 136,373, the plasticizing material of the coating composition may constitute a single plasticizer, or may includea variety. of plasticizers. Plasticizers are substantially non-volatile substances which serve to modify the physical properties .of the cellulose ester film-forming material, including the melting or softening point, compatibility, and/or flow properties. They may be either liquid or solid at temperatures from ambient temperature up to close to imaging temperature, but at least must be fluid at imaging temperature in the complete plasticizing material component of the coating composition.

The plasticizers generally fall into three groups-asregards compatibility with the film-forming material: Par.- tially but incompletely compatible, incompatible, and compatible substances. Certain of the partially compatible plasticizers may be employed as sole plasticizers. Alternatively, two or more plasticizers having individual compatibilities ranging from complete compatibility to complete incompatibility may be employed, so long as the plasticizers together provide the proper balance of compatibility with the film-forming material. When a plurality of plasticizers is employed, it is highly preferable that they be compatible with each other at room tem' perature, forming a single phase mixture thereat, after heating together and cooling, if necessary for mixing.

The plasticizing material or complete plasticizer mix of the preferred coating composition is oleaginous or oily in nature, that is, it contains one or more oleaginous plasticizers. As disclosed in the above-identified earlier patent applications, numerous oleaginous plasticizers may be employed, such as mineral oil, castor oil, hexadecyl alcohol, polypropylene glycol monobutyl ether, polyoxethylene ethers of lanolin alcohols, pentaerythritol tetra-esters of aliphatic acids having from 5 to carbon atoms, trimethylol propane'tri-esters of aliphatic acids having from 5 to 10'carbonatoms; rosin -oil, polyoxethylene polyol fatty acid' esters, and various other natural and synthetic oily materialsp The hydrocarbon resin employed in the present invention maybe oleaginous. Numerous other plasticizers, 'asYdisclosed-in our aforesaid prior applications, also mayfibe" included inythe coating composition.

A plasticizing material or complete plasticizer mix having certain additionalphysical properties has been found to be preferable. Thus, an amorphous plasticizing material having anoptiinum viscosity of about 40-110 Saybolt seconds at 99 C. iszpreferred for imaging purposes. It is preferred for minimizing migration and oiliness that the viscosity. of any separable liquid phase remaining in a cooled meltrof thefcoatingcomposition be at least about 1'0 centipoises at20 C Itis preferred for good aging properties thatthe plasticizing material have a maximumvapor pressure of about 0.1 mm. Hg at 30 C. and be substantially non-hygroscopic. It is preferred for resistance to emulsion type mimeograph inks that the plasticizing'material haveamaximum water solubility of about 1% at 30C.

1 In the present invention, it is generally most advantageous and preferred; for reasons of performance, availability and economy, to employ a mineral oil together with the 'hydrocarbonjresin in the plasticizing material or plasticizer mix having the foregoing character, although others of theabove-describedadditional oleaginous plasticizers may be employed. Mineral oil and/or another of sucholeaginous plasticizers preferably is present in a proportion-in the range of about 10-70%, more preferably -65% byvolume. based on the total volume of the film-forming and plasticizing materials.

' The preferred mineral oils, especially petroleum oils, have'a viscosity below. about 10,000 Saybolt seconds (SUS) at 38 C. and, more preferably, have a viscosity above about 30 Saybolt seconds at 38 C. Mineral oils having anilinepoints ranging from about 15 C. (mixed aniline point) 'to' about 115 C. (straight aniline point) have proven to be satisfactory'. In, general, lower aniline point .oilsare preferredufor use with lower compatibility cellulose esters, i.e., those esters having esterifying acyl groups of lower average molecular weight, and vice versa. "i 1 "Aniline points as 'referred to herein and in the claims are determined in accordance with A.S.T.M. test D- 1012-62,.except Where otherwise specified. Mixed aniline point is the minimumequilibrium solution temperature of 'a mixture of 2 volumes of aniline, 1 volume of sample, and 1 volume of'n-heptane of specified purity. Straight aniline point is the minimum equilibrium solution temperature of a mixture'of 1 volume of aniline and 1 volume of. sample. Where the aniline point of a sample is too high or low;for .direct measurement, a material of known aniline point of opposite magnitude may be mixed with=the sample for. evaluation. The aniline point of the mixture is run, andthe unknown aniline point is determined therefrom employing the formula:

A polymeric hydrocarbon resin is included in the plasticizing material in a preferred proportion of about 3- 60%, more preferably 1030% by volume, based on the total volume of film-forming and plasticizing materials including the resin. The preferred resins are synthetic thermoplastic resins derived from coal tar or petroleum, and more particularly, may be identified as polyindenes. They have a minimum of about 30%, preferably a minimum of 40% by weight of polymerized indenes and coumarones, including, particularly, polymers of indene, coumarone, and monoand dimethyl derivatives thereof as found in the hydrocarbon resin product mixtures. The indenes and coumarones are referred to as bicyclic monomers.

Additionally preferred hydrocarbon resins are polymers having a monomer content that is substantially limited to indenes, coumarones, and styrenes, and may include aliphatic unsaturated monomers, particularly, cyclopentadienes. The styrenes as referred to herein, which are also termed vinyl aromatics, or monocyclic monomers, include styrene and derivatives thereof, such as the monoand dimethyl ringand side-chain substituted derivatives of styrene; ethyl styrene; divinyl benzene; and the like, as found in the hydrocarbon resin mixtures. Divinyl benzene while present in some resins is not a desirable monomer, and preferably, is limited to a maximum of about 3% by weight of the monomer content of a resin. The cyclopentadienes include, particularly, monoand dicyclopentadiene, and monoand dimethyl derivatives thereof, as also found in the hydrocarbon resin mixtures. The cyclopentadienes preferably are limited to a maximum of about 20%, more preferably, a maximum of about 10%, by weight of the monomer content of a resin.

It is further preferred that the hydrocarbon resin employed have a minimum of about 40% by weight of polymerized indenes and coumarones, and a minimum of about by Weight of polymerized aromatic unsaturated or aromatic olefinic monomers, including particularly, the indenes, coumarones, and styrenes, as described above. Any remaining monomer content of the resins may substantially constitute polymerized aliphatic (including cycloaliphatic) unsaturated or olefinic monomers, particularly, the cyclopentadienes as described above. Still further, it is preferred that the monomer content of the resin include at least about 80% of polymerized indenes and coumarones, the balance being substantially (one or more) polymerized styrenes. The latter resins are identified as coumarone-indene resins, commonly produced from the crude heavy solvent naphtha fraction of coal tar light oil, and also from certain carbureted watergas oils.

The hydrocarbon resins useful in the invention may be liquid or solid at ambient temperatures, having softening points (Ring and Ball, A.S.T.M. E-28-42T) preferably in the range of about 5-175 C. The preferred resins of greater durability are solids at ambient temperatures and have softening points above about 50 C., more preferably, above about C.

Useful hydrocarbon resins have a specific gravity (25 C., A.S.T.M. D-71) in the range of about 0969-115, preferably about 1.016-1.145, and more preferably, about 1.1321.145. The useful hydrocarbon resins have a refractive index (11, in the range of about 1.53-4.65, preferably about 1.56-1.64, and more preferably, about 1.62- 1.64. Useful resins in general appear to have iodine numbers (Wijs, A.S.T.M. D-1959) less than about 100, a viscosity (Brookfield) of 1 poise at about 70-270 C., and a viscosity of 10 poises at about 40-220 C. It is preferred -that the color be a maximum of about Gardner 14 (Neville 5), more preferably, Gardner 9 (Neville 2).

The preferred coal tar resins are produced by polymerization of monomers from crude heavy solventnaphthas, preferably boiling in the range of about ISO-200 C. The principal monomers present are indene, methyl indenes,-

coumarone, styrene, vinyl toluenes, and alpha-methyl styrene. The resins may be produced by polymerization of the monomers in the presence of a catalyst, including acid, clay and Friedel-Crafts catalysts. Typical processes are described in Us. Pats. Nos. 1,990,215 and 2,565,222. Preferred coal tar resins include the coumarone-indene resins identified as Cumar resins (Neville Chemical Co.), including grades R-l, R-3, R-S, R-6, LX-509, R-7, R-9, R-l0, R-ll, R-l2 and R-12A. Next in order of preference are Cumar resin grades R-13, R-14, R-l5, R-16, R-17, RH- 17, and R-l9. Additional useful Cumar resin grades include R-21, R-27, R-28, R-29, P- and P-25.

The preferred petroleum hydrocarbon resins are produced by polymerization of by-product monomers obtained by high temperature, low pressure non-catalytic cracking of petroleum naphthas, natural .gas, or gas-oil in the production of ethylene, propylene, butenes, butadiene, and/ or isoprene. The monomers preferably boil within the range of about 100 C. to 300 C., contain as principal polymerizable components indene, methyl indenes, styrene and vinyl toluenes, and also may contain cyclopentadiene compounds. The resins may be produced by Friedel- Crafts polymerization of the monomers, as disclosed, in US. Pat. No. 3,422,053. A preferred resin produced in this manner is Neville LX-1517 (Neville Chemical Co.).

Additional useful hydrocarbon resins include Nevex 100 and Nevex 110 (Neville Chemical Co.), Resin EC-70 and Resin XL-30 (Velsicol Chemical Corp.), and Piccoumaron 410-HL and Piccoumaron 410-L (Pennsylvania Industrial Chemical Corp.). The useful hydrocarbon resins are low molecular weight polymers, preferably having average molecular weights less than about 2,000, more preferably, in the range of about 290-1600, and further preferably, in the range of about 400-1200 (as determined by vapor phase osmometer).

One or more additional plasticizers may be included in the coating composition if desired, where adjustment of one or more stencil properties is sought. Thus, for example, other plasticizing materials are disclosed in our prior applications Ser. No. 136,373 and Ser. No. 27,135, identified above. Also, as disclosed and claimed in co-pending application of the present inventors and Janis E. Wedyck, Ser. No. 253,394 filed May 15, 1972, enhanced durability may be achieved by the use of certain alkylene oxide reaction products of fatty acids and fatty alcohols, which are oleaginous plasticizers, as exemplified herein by the use of a preferred compound identified as Brij 92 (ICI America), described hereinafter. Further, it may be advantageous to incorporate with the coating composition finely divided silica gel, as disclosed and claimed in application Ser. No. 30,341, filed Apr. 20, 1970, by Leonard G. Larson and the present inventors, now US. Pat. No. 3,694,244. Applied with the composition of the present invention, the silica gel provides insurance against blocking, further minmizes oil transfer where less than optimum, and may provide an additional improvement in durability.

It appears preferable that the mixed aniline point of the complete plasticizing material or plasticizer mix in the composition be in the range of about 4-54 C. when employing cellulose acetate butyrate as the film-forming material, and more preferably, in the range of 21-54 C. with the preferred grades of cellulose acetate butyrate. In general, the compatibility of the cellulose ester film-former increases with the extent or proportion of acyl substitution, and the preferred aniline point of the plasticizing material increases with increased film-former compatibility, and vice versa. Thus, for example, the preferred plasticizer mixed aniline point when employing cellulose butyrate valerate, as exemplified hereinafter, is about C. higher than for cellulose acetate butyrate. The hydrocarbon resin employed in the invention preferably has a mixed aniline point in the range of about 30-65 C. more preferably 45-60 C. One or more other plasticizers is blended with the hydrocarbon resin to provide the desired aniline point for the complete plasticizing material.

The specific film-forming and plasticizing materials and proportions thereof are selected on the basis ofthe herein defined properties. The film-forming and plasticizing materials are soluble in a volatile solvent and are also selected and blended in proportions so as to form a sub stantially homogeneous continuous imperforate coating when deposited from a solution thereof, the :coating then being provided on the base. sheet by deposition of the composition thereon from such. solution. Preferably also, the coating is substantially clear, exclusive of the effect of additives other than the active or basic film-forming and plasticizing materials, i.e., additives such as the silica gel, pigments, fillers, and materials incorporated for other purposes. Reference to clarity is also exclusive of. the opacifying effects of materials having an inherentopacity, such as waxy materials, and of the presence of materials which are solid at room temperature and are incorporated above their solubility limts at room temperature. Filmforming and plasticizing materials also are selected and blended in proportions such as to form a stencil sheet coating melting in the range of about 65-180" C.

When the materials satisfy the basic or preferred conditions, the proportions of individual materials then may be adjusted within limits to achieve optimum properties.

The composition of film-forming and plasticizing materials preferably is completely soluble in a volatile solvent at a temperature of below about 60 C., more preferably, at room temperature. The preferred compositions are soluble in organic solvent mixtures of an aromatic hydrocarbon, and an aliphatic ester and/or aliphatic alcohol. The composition is deposited on the base sheet from a solution in such solvent by evaporation of the solvent. The stencil coating formed in this manner is a uniform gel. The gel structure is changed so that the stencil coating is irreversibly physically altered when it is heated to its melting point, and also, at times, when it is heated to the compatibility temperature of-the coating composition although lower than such melting point. Accordingly, the coated stencil base sheet is dried at a temperature below the melting point and the compatibility temperature, preferably at least 5 C. below the lower of the two temperatures.

In producing a stencil having optimum properties according to the invention, the following general sequence of evaluations may be followed:

At a selected proportion of cellulose ester, a mixture of plasticizers of diverse aniline points is combined and their relative proportions adjusted to vary the aniline point of the plasticizer mix until an aniline point optimum for the desired results is ascertained. -In general, higher aniline points lead to better copy quality, slower imaging speed, more oil transfer, lower durability, better sensitivity for typing, and less blocking, and vice cersa for lower aniline points. Theproportion of the cellulose ester then is adjusted for optimum properties. In general, increasing the ester proportion at the same anilnie point lowers the copy quality,"reduces the imaging speed, decreases the oil transfer, increases the durability, reduces the sensitivity to typing, and reduces the blocking, and vice versa for decreasing ester proportions. The adjustment of the plasticizers for optium aniline point then may be repeated with the optimum cellulose ester proportion.

A hydrocarbon resin according to the present invention is then selected and evaluated at various proportions, em ploying the optimum proportion of cellulose ester and with the resulting plasticizer mix at the optimum aniline point. The aniline point and/or thecellulose ester proporother plasticizers, for improving the product in one or more respects, or making the product more attractive commercially, more adaptable to existing equipment or available materials, and so forth. It is also found that variations in the product may be desirable for certain types of ultimate use and/or reproduction equipment.

The stencil sheet may be imaged in a conventional thermographic machine, such as a roller-type copier as represented by Weber Thermal Imager, and a belt-type copier such as a Thermo-Fax Model 45CG Secretary machine A tungsten filament lamp or other suitable source of infrared radiation is employed for imaging. A printed original incontact with the stencil sheet is exposed to radiation substantially instantaneously, i.e., on the order of about 0.03 to 0.1 second, to generate a temperature rise in the image portions of the original from about ambient temperature to a temperature sufficient to produce an imaging temperature in the image portions of the stencil sheet in the range of about 65-180 C.

The coating composition in the stencil sheet is heated to its melting point and is reduced to a flowable condition substantially instantaneously, and a part thereof is absorbed by the absorbent sheet or into adjacent areas of the stencil sheet immediately thereafter, to leave inktransmitting image openings in the stencil sheet. The openings are bridged by the fibers of the stencil base sheet, which is ink-pervious, and the base sheet fibers serve to retain letter centers and the like in place. It is also found that a part of the coating solidifies in the image openings, after melting, and the solidified material in the openings then is in discrete particles, permitting free flow of ink around them when the stencil is employed for mimeograph duplication. After the stencil sheet is imaged, it is seperated from the original and the absorbent sheet for use as a duplicating master.

' In the examples which follow, the coating compositions were formulated in a solvent mixture of (in parts by weight) 50 parts of toluene, 35.8 parts of ethyl acetate, 14.2 parts of ethyl alcohol (95% denatured, U.S. Government Formula C), except where another solvent mixture is indicated. The cellulose ester was dissolved first in the solvent mixture, followed by dissolving the Brij 92 when employed. The hydrocarbon resin and any other plasticizers, except for the mineral oil, were then dissolved. The mineral oil when employed Was added last, with mixing. When a silica gel was incorporated, it was dispersed in a portion of the solvent mixture, added to the solution of film-forming and plasticizing materials, and mixed well. In thismanner, the materials of each coating composition were incorporated in the solvent mixture at a concentration of about 30-35% by weight. Stencil base tissue sheet material made of abaca fiber was coated and impregnated with a coating composition. The tissue weighed 6.7 lbs. per 3,000 sq. ft. The sheet material was coated with the composition by contacting its bottom surface with the surface of a quantity of coating composition in a dish, removing excess fluid by a doctor rod, and drying by hangingthe sheets in the atmosphere at room temperature. The total coated weight of the resulting stencil sheet ranged from 26 to 30 lbs. per 3,000 sq. ft. The thickness of the resulting stencil sheet was about2 A mils.

In addition to the listed ingredients, each coating composition included 0.17 gram of dilauryl thiodipropionate antioxidant per 1 grams of active materials.

Each stencil sheet was assembled with an absorbent sheet for thermal imaging tests, in which imaging speed and copy quality were rated. The absorbent sheet was 10 lb. per 2,880 .sq.v ft. tissue formed of mixed abaca and wood pulp fibers (Grade 5 tissue, Dexter Corporation). Oil smudging of the original image was determined on carbon ribbon copy typed on bond paper, and oil transfer was determined on offset printed stock. Blocking was determined by storing unassembled stencil sheets in contact with each other in foil, at room temperature. Blocking was also determined in most cases by evaluating pinholing upon exposure With a blank sheet of coated paper in a thermal copier. Durability was determined on a Weber Model 50 (Weber Marking Systems) label printer type of mimeograph stencil duplicating machine.

Illustrative materials which may be employed in the invention, and referred to herein, are described as follows:

Cellulose Esters CAB 500-1 is cellulose acetate butyrate grade EAB 500-1 (Eastman Chemical Products) having an average butyryl content of 49.6%, an average acetyl content of 5.5%, a hydroxyl content of 0.1-0.7%, a viscosity of 0.8-1.2 seconds determined by the hereinabove-identified ASTM method, and a melting point range of about 165- 175 C.

CAB 500-5 is cellulose acetate butyrate grade EAB 500-5 (Eastman Chemical Products) having an average butyryl content of 48%, an average acetyl content of 6%, a hydroxyl content of 0.6-1..1%, a viscosity of 4-6 seconds (ASTM), and a melting point range of about 165-175 C.

CAB 381-2 is cellulose acetate butyrate grade EAB 381-2 (Eastman Chemical Products) having an average butyryl content of 37%, an average acetyl content of 13.5%, an average hydroxyl content of 2%, a viscosity of 1-3.5 seconds (ASTM), and a melting point range of 171-184 C.

Half-Second Butyrate (Eastman Chemical Products) has an average butyryl content of 37%, an average acetyl content of 13.5%, an average hydroxyl content of 2%, a viscosity of 0.3-0.5 second (ASTM), and a melting point range of 155-165" C.

Tenth-Second Butyrate (Eastman Chemical Products) has an average butyryl content of 37 an average acetyl content of 13.5%, an average hydroxyl content of 2%, a viscosity of 0.01-0.16 second (ASTM), and a melting point range of about 155-165 C.

CAB 451-1 is cellulose acetate butyrate grade EA B 451-1 (Eastman Chemical Products) having an average butyryl content of 44%, an average acetyl content of 8.5%, an average hydroxyl content of about 1.3%, a viscosity of 1-2 seconds (ASTM), and a melting point range of 150-155" C.

CBV is cellulose butyrate valerate (Eastman Chemical Products) having an average valeryl content of about 46%, an average butyryl content of about 6%, a viscosity of 0.9 second (ASTM), and a melting point of about 120 C.

Silica Gel Syloid 255 (Davison Division, W. R. Grace Company) is silica gel having an oil absorption of about 315 lbs./ 100 lbs., a particle size range of 0.8-12 microns (90%), and an average particle size of about 3-4 microns.

Plasticizing Material Mobilsol L (Socony Mobil Oil Co.) is 'a refined naphthenic petroleum oil having a viscosity of 61 Saybolt seconds (SUS) at 38 C., a straight aniline point of 74 C., an API gravity of 25.7, and a distillation range of 254-370 C. (100%).

Brij 92 (ICI America) is polyoxyethylene ether of oleyl alcohol (2moles of ethylene oxide) having. an HLB. (Atlas Hydrophile-Lipophile Balance) of 4.9, an acid number of 1.0 max, and a hydroxyl number of'160-l80.

It has a typical viscosity of approximately 30centipoises at 25 C. .(ASTM No. D445-53 T), and a theoretical mixedaniline point of -2.8 C.

Staybelite Ester 5 (Hercules, Inc.), is a glycerol esten of hydrogenated rosin purified by steam distillation, typi-,

cally having a softening point (Hercules drop method) of 81 C., an acid number of 5, a specific gravity of- 1.06 at 25 C., and a mixed aniline point of 24.4 ,C. V

Benol (Witco Chemical Company) is a white mineral oil typically having a viscosity of 100 Saybolt seconds at 38 C., a theoretical aniline point of 182 C., an API gravity of 34, a distillation range of from 658 to 822 F. (100%), an ASTM cloud point of -10 C., an ASTM 12 The preferred resin grades R-l, R-3, R-5, R-6, LX-509, R-7, R-9, R-lO, R-11, R-12 and R-12A typically have the following more specific monomer composition:

pour point of '-12 C., and a flash point of 199 C.

Conoco DBOL (Continental Oil Company) is dedecylbenzylchloride (94.5%) having a viscosity of 101 Saybolt seconds at 38 C. and a mixed aniline point of 18 C. Range of Average Texanol Isobutyrate (Eastman Chemical Co.) is 2,2,4- p p t p po t s. percent by percent by trimethyl pentanediol dnsobutyrate havmg a vlscosity of Monomer weight weight 9 centipoises at 25 C., and a mixed aniline point of 8 C. Indene 79 H0 2 85 Flexol Plasticizer P (Union Carbide d Carbon Meth i'ih'ifiiIIIIIIIIIIIIIIIIIIIIIIIIIIII 0-63 210 Corp.) is di (isodecyl) 4,5-epoxy tetrahy-drophthalate havgtoumamne 119-104) a yrene 0 0 mg a viscosity of 184 centipoises at 20 C. and a mixed Vinyl toluenes a2-11.5 7.1 aniline point of 7 C. Alpha-methyl styrene 0-1.7- 0.2

Bis-alpha-methyl benzyl ether (Union Carbide and Carbon Corp.') has a viscosity of 16.7 centipoises at C. and a mixed aniline point of 22 C.

Atmul 122 (ICI America) is a solid of melting point 20 approx. 52 C., composed of monoand diglycerides of v edible fats or oils, and containing a minimum of 54% The foregoing preferred resin grades R-l through R- monoglyceride (alpha form), and having a theoretical 12A are designated collectively as Type I resins. Resin mixed aniline point of --1 C. grades R-13, R-14, R-15, R-16, R-17, RH-17, and R-19 Conoco Parafiins (Continental Oil Co.) are normal C are designated as Type II resins. Resin grades R-2l, R-27, to C paraflins, containing 978% by weight of n-parafiins R-28, R-29, P-lO and P-25 are designated as Type III and 2.2% by weight maximum aromatics. The composiresins. The resins of the several types typically have the tion has a specific gravity of 0.78 at 16 C., a melting point following physical properties:

Type I Type II Type III 1 Soitening point, C 98- 5 56-105 7-48 2 Specific gravity, 25C- 1.3211.145 1. 016-1. 127 ease-1.099 3 Iodine number 51- 5 48- 46-84 4..- Mixed aniline point, C 46-56 32-62 33-64 5 Molecular weight 540-1,150 400-800 290-530 6 Temperature at 1 poise viscosity, C- 186-267 127-216 71-138 7 Temperature at 10 poises viscosity, 151-2 102-171 44-98 a Refractive index, 25 0 1. 622-1. 634 1. 561-1.631 1. 533-1. 61

of 8 C., a viscosity of 2.7 centistokes at 38 C., and a mixed aniline point of 82 C.

Individual Cumar resins employed in the examples herein exhibited the following physical properties:

R-9 RH-17 R-19 LX- 1 Softening point, C-.- 111. 5 71. 5 56 160-165 2..- Specific gravity, 25 C- 1.141 1. 123 1. 016 1. 134 3..- Iodine number.. 51.2 63.1 53.5 58 4 Mixed aniline point, C 46. 8 42. 0 58 55. 8 5 Molecular weight 591 1, 090-1, 148 6 Temperature at 1 poise viscosity, C. 267 7 Temperature at 10 pulses viscosity, 0.. 220 8 Refractive index, 25 C- 1. 634

Terpex Rosin Oil (SCM Glidden-Durkee) is a terpenic hydrocarbon oil having a specific gravity of 0.945 at 155 C., a Gardner-Hol-dt viscosity of H-K at 25 C., and a mixed aniline point of 54 C.

Hydrocarbon Resins Cumar coumarone-indene resins (Neville Chemical Co.) identified by grade designations R-l, R-3, R-S, R-6, LX-509, R-7, R-9, R-IO, R-ll, R-l2, R-12A, R-13, R-14, R-lS, R-16, R-17, RH-17, R19, R-21, R-27, R-28, R-29, P-10 and P-25 typically have the following monomer composition:

- Range of proportions,

Monomer by weight Indene 41.7-90.2 Methyl Indenes -2 0-6.3 Coumarone 0-10.0

Styrene 014.8 Vinyl Toluenes 3.2-37 .0 Alpha-Methyl Styrene 06.5

Methods of analysis for the above-numbered properties of the Cumar resins were as follows:

Neville LX-1517 (Neville Chemical Co.) is a petro; leum hydrocarbon resin produced by polymerization of petroleum naphtha fractions boiling in the range of 13 300 C. and having the following typical monomer composition and physical properties: i e

. Proportion, Monomer percent by weight Indene r 24 Methyl Indenes 19 Styrene 19 Vinyl Toluenes ....'.n.;. 23 Alpha-Methyl Styrene u 3 Divinyl Benzene 2-3 Other C -Styrenes 9-10 J i "Physical Properties .1. Softening Point, 103 2. Specific Gravity, 25 C 1.062 3. Iodine Number 19-27 4. Mixed Aniline Point, C. 39.9 5. Molecular Weight 840 6. Temperature at 1 poise viscosity, C 205 7 Temperature at .10poises viscosity, C 161 8. Refractice Index, 25 C 1.593

"Nevex 100 and 110 (Neville Chemical Co.) are predominantly aromatic hydrocarbon resins having the following typical physical properties:

1. Softening Point, C. 102-109 2. Specific Gravity, 25 C. 1.112-1.116 3..Iodine Number 54-60 4. Mixed Aniline Point,- C. 44.1-45.2 5. Molecular Weight 602-699 '16. Temperature at 1 poise viscosity, C 184-192 7. Temperature at 10 poises viscosity, C. 147-154 '8. Refractive Index, 25 C. 1.621-1.622

, Piccoumaron 410-HL (Pennsylvania Industrial Chemical Corp.) is a hydrocarbon resin copolymer of primarily in'dene and vinyl aromatics (primarily styrene), in a weight ratio of 2.2-2.3 parts of indene per part of vinyl aromatics, having a softening point of 110-115 C., a specific gravity of 1.10, a refractive index of 1.63-1.64, a theoretical mixed aniline point of 46 C., an iodine number of 36, and a viscosity (Brookfield) of 1 poise at 195- 200 C. and 10 poises at 165-170 C.

Resin EC-70 (Velsicol Chemical Corp.) is a hydrocarbonresin copolymer of 60% indenes, 10% coumarones and 30% styrene (estimated proportions by weight), typically having a softening point (Ring and Ball) of 112- 118 C.,"a specific gravity of 1.08-1.11 (16 C.), a theoretical mixed aniline point of 48C., and an iodine number of 80 max.

Resin XL-30 (Velsicol Chemical Corp.) is a hydrocarbon resin copolymer including indene and styrene, typically having a softening point (Ring and Ball) of 102- 1'07C.,a 'specificgravity of 1.04-1.07 (16 C.), a refractiveiindex of 116, a theoretical mixed aniline point of 40 C., a saponification number of 0-2, and an acid number of 0-2.

The following examples illustrate stencil sheets having various coating compositions according to the invention. In the examples, the aniline points refer to measurements on the mixture of plasticizers, exclusive of the cellulose ester, silic'a'gel, pigments, and solvents. The volumetric relationships are significant only for the film-forming and plasticizing materials, which constitute the herein-termed active materials, and are calculated only for such materials; It will be understood that the invention is not limited to the examples, which are merely illustrative, or to the materials, proportions, conditions and procedures set forth therein.

' EXAMPLE 1 Three coating compositions identified as A, B, and C were deposited on stencil base tissue, providing a total coated weight of about 26 lbs. per 3,000 sq. ft. with compositions A and B, and 27.5 lbs. per 3,000 sq. ft. with composition C. Compositions A and B varied in the grade of cellulose acetate butyrate, and compositions A and C 1 4 differed in that the latter included. silica gel. The

compositions were as follows: i

EXAMPLE 1 1.

Composition A B C All Proportion, Proportion, percent by parts by 1 volume weight Material:

CAB 500-1 16.85 16. 85 19. 9 CAB 500-5 16.85 19. 9 Cumar R-9 20.00 20. 00 20. 00 22. 4 Mobilsol L. 41. 70 41. 70 41. 70 38. 1 Bn'j 92"... 21. 45 21. 45 21. 45 19. 0 Syloid 255 l 4. 0

Temperature, 0.

Mixed aniline point of plasticizer mix 48 48 48 Compatibility temperature. 130 127-130 130 Melting point of stencil coating 116-127 128-135 116-127 1 Composition C only.

Under several types of test conditions, the thermal imaging speeds of the three stencils were rated generally good, and their copy quality ratings were generally good.

Composition A had an oil smudging rating of very good and an oil transfer rating of good. Composition B had oil smudging and oil transfer ratings of good. Composition C, containing silica gel, was improved over composition A, having the ratings excellent for oil smudging and very good for oil transfer. None of the stencils exhibited blocking, for excellent ratings in this respect.

The durability of each stencil was high. The stencils from compositions A and C had desirable sensitivity for typing stencils, whereas typing sensitivity of the stencil from composition B was low. The stencil from composition C had excellent aging properties, determined upon storage for six months at 49 C.

The Cumar R-9 hydrocarbon resin employed in this and succeeding examples, as a preferred resin, and having the composition and properties described hereinabove, was made by the PB-Sulfuric process essentially as described in US. Pat. No. 1,990,215, from feed crude heavy solvent naphtha having the following typical properties (ASTM D-850):

Specific Gravity, l5.6/15.6 C. 0.965

Distillation, C.:

First drop 164 5% 172 10% 174v 50% 178 182 185 Decomposition 194 EXAMPLE 2 The following compositions A and B were compared when deposited on stencil base tissue at respective total coated weights of about 27 and 2.8 lbs. per 3,000 sq. ft.:

The essential change in compositionA .from'composition B was the replacement of the plasticizer Staybelite Ester No. by the hydrocarbon resin plasticizer Cumar .R-lO pursuant to the PICSiltjlIlYfiDIiQll, Theirnaging speed increased from generally fair with the stencil from composition- B to from'good to very good with the stencil from composition A. Copy quality was good in both cases. r v

For composition oil transfe r fair. Oil smudging and 'oil'tran'sfefboth were rated excellent employing composition A. Blocking was excellent and durability was high in both cases. Typing sensitivity was similar and acceptable for both compositions.

B, oil smudging was rated good and 1 Composition A 13" L o D" Material:

Proportion, pernentby volimie Hall-second butyrate or tenth- I Mixed aniline point of plasticizer Temperature,f?

Coating composition solvent; 80% toluene, ethanol (95%), by weight;

EXAMPLE 3 The following coating composition was deposited on stencil base tissue to provide a total coated weight of about lbs. per 3,000 sq. ft.:

Except for composition C, havingvery high durability with low sensitivity, the stencil sheets are suitable-for Material Volume percent imaging by typewriter as. wellv as thermographically. CAB 500-1 16-0- .EXAMPLE 5 Cumar R-9 4.0. n Mobilsol L 38.9. The following coating COIIIPOSItIOIIS'WheII dGPOSltadE on Brij 92 37.8. stencil base tissue to provide a total-:rcoatedweight of Titanium Dioxide grind (70% by 26 /2 to 28 /2 lbs. per 3,000.sq. ft.:resulted in improved weight in Castor Oil) 2.5. stencil sheets according :to.-the- -invention,-suitable=for Chrome Yellow grind by imaging both thermographicallyandby typewriter: 1% weight in Castor Oil) 0.8. 1. Syloid 255 3 lbs./1bS.Of "T remaining materials. 55

Composition 2" A B ofln nf'n 'o Proportion, percent by volume r Material:

CAB 500-1 Cumar LX-509 Nevex 100 Piceoumaron 410-HL. CumarR-l 20.00

Cumar R- .00 Cumar R-27 CumarP-IO--- 0. MobilsolL 37.60 43.40 42.30 21.70 20. 40 34.70 25,60 Brij92 19.70 18.60 22.00 41.45 42.75 27.30 36.40

I H I Temperature,C. I Mixedanilinepolntolplasticizermix. 481 48 48 31. 31 37 31 Compntibilitytemperatur 127 17 w I EXAMPLE 6 The following coating compositions when deposited on stencil base 'tissue to provide atotal coated weight of 26 to'2'8' lbs. -per-3,000 sq.ft; resulted in improved stencil sheets according to'the invention:

'EXAMPLE 7 :,.The following coating compositions when deposited on stencil; base, tissue,-to,provide ,a; total coated weight of 26 to 28 /z lbs. per, 3,-,000 sq, ft. resulted in improved stencil sheets according ,to the invention zu Composition f A B o D E ,lfroportion, percent by volume Material:

CAB 500-1. 15.70 25 15.70 16.85 16.85 Currier R-9 10.00 20 00 20.00 20.00 20.00 Mobilsol L 49. 00 .Conocoparaffins 38. 30

Terpex rosin oil- 60 iii 92 l...l.f.t 25.80 18.70 26 00 0.55 y rolyox ethylene po y,o a

, acid ster... 63.15

i I I Temperature, C.

i ili e olnt of lastlcizer Mxgd an n p p 48 48 48 40 mix. Compatibility temperature 93 Polyoxyethylene (40) sorbitol septaoleate, having an HLB value of 9,'an acid number of 812, an hydroxyl number of 22 38, a sapomfication number of 100l10, a typical viscosity of 175 centipotses at 25 C., and a theoretical mixed aniline point of 37 C.

1 We claim; 7 v w 1. Ina stencil sheet including an ink-pervious base sheet, and an ink-impervious-coating thereon of a heatflowable composition of thermoplastic film-forming materialcomprising acellulose organic ester, and plasticizingtmaterial partiallybut incompletely compatible with said filmef orming material, the. improvement which comrises P a thermoplastic polymeric hydrocarbon resin included in said plasticizing material in a proportion of about 360% by vo1ume basedbn the total volume of the film-forming and plasticizingmaterials, said resin having a total content of polymerized indenes and coumarones of at least about 30% by weight, a maximum content of polymerized divinyl benzene of about 3% by weight, and a maximum content of polymerized cyclopentadienes of about 20% by weight, and said resin having a mixed aniline point of about 30-65 C., a softening point of about 175 C., and Brookfield viscosities of 1 poise at about 70 270 C. and poises at about 40-220" C.

2. A stencil sheet as defined in claim 1 wherein the monomer content of said resin is substantially limited to indenes, coumarones, styrenes, and aliphatic unsaturated monomers, and said resin has a. total content of polymerized indenes and coumarones of at least about 40% by weight, and a total content of polymerized indenes, coumarones, and styrenes of at least about 80% by weight.

H 3. A stencil sheet as defined in claim 1 wherein said resin is a coal-tar coumarone-indene resin having a-total content of polymerized indenes and coumarones of at least about by weight and the balance substantially polymerized styrenes.

4. A stencil sheet as defined in claim 3 wherein the softening point of said resin is in the range of about C.

5. A stencil sheet as defined in claim 1 wherein said cellulose ester is selected from the group consisting of cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate valerate, cellulose propionate butyrate, cellulose propionate valerate, cellulose butyrate valerate, cellulose propionate, cellulose butyrate, and cellulose valerate.

6. A stencil sheet as defined in claim 1 wherein said plasticizing material also includes a mineral oil.

7. In a stencil including an ink-pervious base sheet, and an ink-impervious coating thereon of a heat-flowable composition of thermoplastic film-forming material comprising a cellulose organic ester, and plasticizing material partially but incompletely compatible with said film-forming material including a mineral oil, the improvement which comprises a thermoplastic polymeric hydrocarbon resin included in said plasticizing material, said resin having a total content of polymerized indenes and coumarones of at least about 30% by weight, a maximum content of polymerized divinyl benzene of about 3% by weight, and a maximum content of polymerized cyclopentadienes of about 2.0% byweight, and said resin having a mixed aniline pointof about 30-65 C., a softening point of about 5-175" C., and Brookfield viscosities of 1 poise at about 70-270 C. and 10 poises at about 40220 C.,

the proportions of said materials being about 5-45% of said ester, about 3-60% of said resin, and about 10-70% of said mineral oil, in proportions by volume based on the total volume of the film-forming and plasticizing materials.

8. A stencil sheet as defined in claim 7 wherein said cellulose ester is cellulose acetate butyrate.

9. A stencil sheet which comprises an ink-pervious base sheet, and an ink-impervious coating thereon of a heatflowable composition of thermoplastic film-forming material comprising a cellulose ester selected from the group consisting of cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate valerate, cellulose propionate butyrate, cellulose propionate valerate, cellulose butyrate valerate, cellulose propionate, cellulose butyrate, and cellulose valerate, and

plasticizing material partially but incompletely compatible with said film-forming material including a thermoplastic polymeric hydrocarbon resin having a total content of polymerized indenes and coumarones of at least about 30% by weight, a maximum content of polymerized divinyl benzene of about 3% by weight, and a maximum content of polymerized cyclopentadienes of about 20% by'weight, and said resin having a mixed aniline point of about 30-65 C., a softening point of about 5-175 C., and Brookfield viscosities of l poise at about 70270 C. and 10 poises at about 40-220" C.,

the proportions of said materials being about 5-45% of said ester and about 360% of said resin, in proportions by volume based on the total volume of the film-forming and plasticizing materials,

said composition forming a substantially homogeneous single phase melt, and when cooled from the melt having a cloud point in the range of about 50-180 C., and forming a two-phase mixture at room temperature, at least one phase of said mixture incorporating substantial proportions of both said filmforming material and said plasticizing material,

said composition being soluble in a' volatile solvent and forming a substantially homogeneous continuous imperforate coating when deposited from a solution thereof, and said coating being provided on said base sheet by deposition of said composition thereon from a solvent solution of the composition and removal of solvent therefrom, the melting point of said coating being in the range of about 65-180 C., said coating further becoming fiowable and irreversibly physically altered when heated to its melting point for forming ink permeable image areas in the cooled stencil sheet.

10. A stencil sheet as defined in claim 9 wherein said cellulose ester has a minimum total butyryl and valeryl content of about 35% by weight, and a maximum hydroxyl content of about 4.7% by weight.

11. A stencil sheet as defined in claim 10 wherein the monomer content of said resin is substantially limited to indenes, coumarones, styrenes, and aliphatic unsaturated monomers, and said resin has a total content of polymerized indenes and coumarones of at least about 40% by weight, and a total content of polymerized indenes, coumarones, and styrenes of at least about 80% by weight.

12. A stencil sheet as defined in claim 11 wherein said plasticizing material also includes a mineral oil in a proportion of about 10-70% by volume based on the total volume of the film-forming and plasticizing materials.

13. A stencil sheet which comprises an ink-pervious base sheet, and an ink-impervious coating thereon of a heat-fiowable composition of thermoplastic film-forming material comprising cellulose acetate butyrate having a minimum butyryl content of about 35% by weight and a maximum hydroxyl content of about 4.7% by weight,

plasticizing material partially but incompletely compatible with said film-forming material including (a) a thermoplastic coal-tar coumarone-indene resin having a total content of polymerized indenes and coumarones of at least about 80% by weight and the balance substantially polymerized styrenes, a maximum content of polymerized divinyl benzene of about 3% by weight, and a maximum content of polymerized cyclopentadienes of about 20% by weight, and said resin having a mixed aniline point of about 30- 65 C., a softening point of about 90-175 C., and Brookfield viscosities of 1 poise at about 70-270 C. and 10 poises at about 40-220 C., and (b) a mineral oil, the proportions of said materials being about -45% of said cellulose acetate butyrate, about 3-60% of said resin, and about -70% of said mineral oil, in proportions by volume based on the total volume of the film-forming and plasticizing materials, said composition forming a substantially homogeneous single phase melt, and when cooled from the melt having a cloud point in the range of about 50-180 C., and forming a two-phase mixture at room tem- 20 perature, at least one phase'of said mixture incorporating substantial proportions of both saidfilmforming material and said plasticizing material, said composition being soluble in'a volatile solvent and forming a substantially homogeneous continuous imperforate coating when deposited from a solution thereof, and said coating being provided on said base sheet by deposition of said composition thereon from a solvent solution of the composition and removal of solvent therefrom,-the melting point of said coating being in the range of about'65-l80 C., saidcoat ing further becoming flowable and irreversibly 'phy's ically altered when heated to its melting point for forming ink-permeable image areas in the cooled stencil sheet. a r 1 j 14 A stencil sheet as defined in claim 13 containing, in proportions by volume based on thetotal volume of the film-forming and plasticizing materials, about 14- 30% of said cellulose acetate butyrate, about 10-30% of said resin, and about 15-65% of said mineral oil, said cellulose acetate butyrate having a'minimum butyryl con= tent of about 44% by weightand a maximum hydroxyl content of about 2% by weight.

15. In a method of making an imaged stencil sheet employing a stencil sheet which includes an ink-irnpervious layer of a heat-fiowable composition, wherein image areas of the stencil sheet are subjected to heat generated" in adjacent image areas of an original by infrared ray absorption to render the composition flowable in" the" stencil sheet image areas and the composition is caused to flow therefrom and thereby form corresponding inktransmitting image openings in the stencil sheet, the improvement which comprises employing as said stencil sheet the stencil sheet of claim 1..

16. A stencil sheet as defined in claim 1 wherein said resin has a total content of polymerized coumarones of up to about 10% by weight. 1

17. A stencil sheet as defined in claim 14 wherein said resin has a total content of polymerized coumarones of up to about 10% by weight.

References Cited UNITED STATES PATENTS MURRAY KATZ, Primary Examiner US. Cl. x.R.

Patent No 3 Dated lflv ntofl Bror E. Anderson and Margery L. Schick It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 27: Change "melts" to -----me1t--;

8, 54: Change "cersa" "to versa--;

37: Change "0.01" to 0.07--'--;

11, l 7 Chsnge "ded ecy l" to --dodecy1--;

12, third table therein: Change the heading "LX-50" to --Lx-509--.

SignedCand sealed this 4th day of February 1975.

C (SEAL) Attest: v

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents po'wso E USCOMM-DC wanoo fi' U,S. GOVERNMENT PRINTING OFFICE: I9! 0-365-331. 

